Process for preparing unsaturated alcohols



Patented Nov. 30, 1948 PREPARING' UNSATURATED ALCOHOLS PROCESS FOR Glen H. Morey, Terre Haute, Ind; assignorito Commercial Solvents Corporation, Terre Haute, Ind.', a. corporation of Maryland No Drawing. Application January 22,1944, Serial No. 519,346

1 This invention relates to the preparation of aliphatic unsaturated monohydric alcohols, and more particularly to a method for preparing such alcohols by the controlled dehydration of saturated clihydric aliphatic alcohols having a single tertiary hydroxyl group.

The invention relates more particularly to the partial dehydration of saturated diols having the following structural formula:

in which R and R are alkyl radicals, R and R are hydrogen or alkyl radicals and n is an integer from 1 to 4 inclusive. In this formula it will be observed that the hydroxyl (OH) group at the left-hand side of the formula is that of a tertiary alcohol being attached to a tertiary carbon atom, that is, to a carbon atom which is linked to three other carbon atoms. The hydroxyl on the right side of the formula is either secondary, when R is alkyl, that is, on a carbon atom attached to two other carbon atoms, or primary, when R is hydrogen, that is, on a carbon atom attached to only one other carbon atom.

Aliphatic dihydric alcohols of the class described have been subjected to dehydration in the past, with the. loss of "both hydroxyls as water to form unsaturated compounds (dienes) and their dimers as the major products of the reaction. For example, dehydration of 2'-methyl-2,4-pentanediol by the process of my copending application, Serial No. 423,576, filed August 31, 194(2 and now abandoned, and 'Patent No. 2,368,068 dated January 23, 1945, results in the formation primarily of Z-methylpentadiene in one case and primarily of dimers of 2-methylpentadiene in the other case.

It is an object of'the present invention to pre pare unsaturated aliphatic monohydric alcohols form dihydric alcohols having a single tertiary hydroxyl group and another hydroxyl group while the primary or secondary .hydroxyl' group facid as the dehydrating catalyst.

remains for the the most part unchanged in the molecule after the partial dehydration.

Astill further object is to prepare isomeric unsaturated, monohydric alcohols of the following probable structural formulas:

I 4 OH in which R and R are valkyl radicals, R and R are hydrogen or alkyl radicals, and n is an integer from 1 to 4 inclusive.

Another object is to provide aprocess forthe partial dehydration of the dihydric alcohols describediin which the resulting product comprises a greatly preponderant proportion of unsaturated monohydric alcohol, and a minor proportion of the diene. 1

A still further object is to provide a process for preparing 4-methylpentene-2eol by controlled dehydration of Z-methyl-2,4-pentanediol.

Other objects will be apparent from the specification and claims. i

In my copending application, Serial No. 519,345, filed Jan. 22, 1944, and now abandoned, I have described a method for preparing unsaturatedalcohols fromydiols by controlled dehydration of the diol utilizing p-toluenesulfonic This treatment resulted in the formation of a miirture of the unsaturated alcohol andgthe diene, with the unsaturated alcohol present in'a somewhat larger proportion than the diene.

I have now foundthat I can'prepare the type oi unsaturated alcohols described," bycontrolled dehydration of thediols accordingto an improved process in which the unsaturated alcohol is formed in a greatly -preponderant amount while the diene is formed-in very much lesser quantities down to rather insignificant amounts.

According to mypresentinVention, 'I utilize any of the previously known dehydrating agents which do not tend to polymerize the resulting product, that is, I may utilize the, pll fonic acid of my acknowledged copending application, or the iodine dehydrating compounds of my Patent No. 2,368,068. The improvement in procedure resulting in the surprisingly increased yields comprises first adding a small proportion of water to the diol before starting the dehydration step. A dehydration catalyst is then added, and the mixture is distilled. The oil layer of the distillate is drawn off while continuously returning the water layer to the distillation vessel.

The amount of water added may be relatively small, just suflicient to insure control of the dehydration in the initial stages, as water is formed as a reaction product of the process. If too large an initial amount is added, the reaction is slowed down and requires a longer period to go to completion. I therefore prefer to add not over about 20% of Water, preferably less than by weight, based on the weight of the diol used.

The dehydrating agents which are suitable for use in my improved process are p-toluenesulfonlc acid, iodine, aniline hydroiodide, and hydrogen iodide. Only a very small percentage is sufficient to catalyze the dehydration about 0.1% to 1.5% by. weight, based on the weight of the diol being required.

In practicing my invention, I add to the dihydric alcohol to be dehydrated a small but effective percentage of water, place the mixture in a distillation vessel in the presence of a relatively small proportion of dehydration catalyst, and heat so that the material distills rapidly. The product which distills consists of a greatly preponderant portion of the unsaturated alcohol with a minor portion of the diene.

It is surprising that the addition of water to a product to be dehydrated should improve the dehydration process. Although it is not known just what function the water plays, it is possible that its effect is such as to inhibit the dehydration of the primary and secondary hydroxyl group, but insuflicient to inhibit the dehydration of the tertiary hydroxyl group which'occurs more easily. Whatever the explanation may be, my improved process enables 'me to obtain mixtures of unsaturated alcohol and diene in which the proportion of alcohol greatlypredominates, ranging from twice as much alcohol as diene to four times or more the amount of alcohol to diene.

As illustrative of my invention, the following examples are given:

EXAMPLE I Iodine as catalyst 2740 parts by weight of 2-methyl-2,4-pentanediol (23.2 moles) are mixed with 200 parts by weight of water and 4 parts by weight of iodine are added. The material is distilled in an apparatus whereby the oil layer in the distillate is collected and the water layer is continuously returned to the kettle. Theoil layer is fractionated, resulting in yields of products as follows:

p-Toluenesulfonic acid as catalyst 2740 parts by. weight of 2-methyl-2,4-pentanediol and 200 parts byweight of water are placed in a distillation vessel along with 3 parts y weight of p-toluenesulfonic acid. The oil layer of the distillate is collected and the water layer is returned to the kettle. On fractionation of the oil layer, the following yields of products are obtained:

Per cent Z-methylpentadiene 15.6 4-methylpentene-2-ol 60.2 Dimer of the diene 12.1

Total 87.9

While the above describes the preferred embodiments of my invention, it is to be understood that departures may be made therefrom withinthe scope of the specification and claims.

What is claimed is:

1. In a process for the preparation of 4-methyl-- pentene-2-ol isomers in proportions of at least;

twice the quantity of the concomitantly formed.

dienes, the steps which comprise mixing Z-methy1-2,4pent'anediol with a relatively small but effective percentage proportion of water not substantially exceeding about 10 per cent by Weight, adding thereto a dehydration catalyst selected. from the group consisting of p-toluenesulfonic: acid, iodine, aniline hydroiodide and hydrogen iodide, rapidly distilling the mixture, condensingthe distillate whereby a Water layer and an oil layer are formed, continuously returning the water layer to the distillation vessel throughout the. distillation process, while collecting the oil layer, and recovering the 4-methylpentene-2-ol isomers; from the oil layer.

2. In a process for preparing a mixture of organic compounds comprising a greatly preponderant proportion of isomeric monohydric unsaturated alcohols and a lesser proportion of the corresponding dienes, the steps which comprise adding a relatively small but effective percentage of water not substantially exceeding about 10 per cent by weight to an aliphatic dihydric alcohol of the following structural formula:

on 4 on in which R and R. are alkyl radicals, It and R are selected from the group consisting of hydrogen and alkyl radicals and n is an integer from i to 4 inclusive, adding thereto a dehydration catalyst selected from the group consisting of p-toluenesulfonic acid, iodine, aniline hydroiodide and hydrogen iodide, rapidly distilling the mixture, condensing the distillate whereby a water layer and an oil layer are formed, continuously returning the water layer to the distillation vessel throughout the distillation process, while collecting the oil layer, and recovering the isomeric monomeric monohydric unsaturated alcohols.

3. In a process for preparing a mixture of organic compounds comprising a preponderant proportion of monohydric unsaturated alcohols of the following structural formulas:

Y and are selected from the group consisting of hydro- 9 gen and alkyl and n is an integer from 1 to 4, REFERENCES CITED inclusive and a lesser proportion of the corresponding di-enes the steps which comprise adding The following references are of record in the a relatively small but effective percentage of wafile Of this P t ter not substantially exceeding about per cent 5 UNITED STATES PATENTS by Weight to an aliphatic dihydric alcohol of the following structural formula: Number Name Date R2 H Re. 19,194 Guenther et al June 5, 1934 (E (B v 1,164,647 Hlbbert Dec. 21, 1915 2,184,164 Mueller-Cunradi et a1. Dec. 19, 1939 of; R4 H 2,229,652 Halbig et al Jan. 28, 1941 in which R and R are alkyl radicals, R and R FOREIGN PATENTS are selected from the group consisting of hydro- Number Country Date gen and alkyl radicals and n is an integer from 413 909 Great Britain July 26 1934 1 to 4, inclusive, adding thereto a small proportion 421218 Great Britain July 1937 of a dehydration catalyst selected from the group 4831781 Germany om 1929 consisting of p-toluenesulfonic acid, iodine, aniu line hydroiodide, and hydrogen iodide, heating OTHER REFERENCES the mixture to distillation temperature, distilling Duveen at a Chemical society Journal rapidly and condensing the distillate to form a 20 (British) 1936 pages 145143 water layer and an oil layer while continuously KyriskideS: ir Am Chem n V01 36 pages returning the water layer to the distillation vessel 9914 (1914) throughout the distillation process, and there- Bachman at at Chem Soc. I: Vol 64 after recovering the unsaturated alcohols from pages 787430 (1942) the distillate.

GLEN H. MOREY. 

